Poly(arylene sulfide) resins (hereinafter abbreviated as "PAS resins") such as poly(phenylene sulfide), poly(phenylene ketone sulfide) and poly(phenylene sulfone sulfide), which have both arylene groups and sulfide groups in their molecules, are engineering plastics excellent in heat resistance, mechanical properties, chemical resistance, flame resistance, electrical properties, molding and processing ability, and the like, and used in wide fields such as electrical and electronic equipments and parts, automotive equipments and parts, and chemical equipments and parts.
The PAS resins however tend to form corrosive gases such as sulfur dioxide when heated to an elevated temperature, and hence involve problems that metallic portions of processing machines, molds and the like are corroded upon their molding and processing, or metal contacts, metal parts of inserts and the like in molded products are corroded. For example, the usual processing machine is made of an iron-based material and hence tends to suffer from chemical corrosion when coming into contact with a PAS resin melted upon its molding. On the other hand, the molded products thereof also become liable to color. The corrosion of a mold causes a great economical loss because the mold is expensive, and moreover makes it difficult to precisely mold. The corrosion of a metal contact in a relay making use of a PAS resin as a base causes a contact failure. The corrosion of a metal part of an insert works out the degradation of solderability at the metal part of the insert. When a PAS resin, which tends to produce a corrosive gas, is used as a sealant for an electronic part, the reliability of the electronic part is lowered.
In order to solve such corrosive problems involved in the PAS resins, it has been proposed to blend various kinds of corrosion inhibitors.
There have been proposed, as corrosion inhibitors for various PAS resins, for example, the hydroxides or carbonates of alkali metals (U.S. Pat. No. 4,017,450), hydrotalcite (Japanese Patent Application Laid-Open Nos. 186561/1985 and 218754/1990), the oxalates of metals selected from Groups IA, IIA and IIB of the periodic table (U.S. Patent No. 4,178,276), .gamma.-alumina (Japanese Patent Application Laid-Open No. 241962/1987), zinc oxide (Japanese Patent Publication No. 45711/1988 and Japanese Patent Application Laid-Open No. 164961/1992), the hydroxides or oxides, or aromatic carboxylates of Group IIA metals of the periodic table, or aromatic carboxylates of Group IA metals of the periodic table (Japanese Patent Application Laid-Open No. 109850/1987), metal aluminates (Japanese Patent Application Laid-Open No. 295955/1987), zinc carbonate and/or zinc hydroxide (Japanese Patent Application Laid-Open No. 105857/1990), lithium sulfite (Japanese Patent Application Laid-Open No. 36264/1990), at least one element selected from zinc, lead, magnesium, manganese, barium and tin (Japanese Patent Application Laid-Open No. 205445/1982), the phosphates of Group IIB metals of the periodic table (Japanese Patent Application Laid-Open No. 161457/1992), the metaborates or tetraborates of Group IA or IIA metals of the periodic table, and the like (U.S. Pat. No. 4,212,793), ammonia precursors such as urea (U.S. Pat. No. 4,115,344), sodium nitrite (U.S. Pat. No. 4,214,021), alkali metal arylalkanates (U.S. Pat. No. 4,237,039), calcium carbonate (Japanese Patent Application Laid-Open Nos. 196858/1990 and 143958/1991), and alkali metal nitrites, benzoates or phthalates; ammonium chromates, benzoates or phthalates; mixtures of alkali metal chromates and alkali metal borates (U.S. Pat. No. 4,064,084).
However, the conventionally-known corrosion inhibitors involve, for example, the following drawbacks. The corrosion-inhibiting effect is insufficient (calcium carbonate, .gamma.-alumina, zinc oxide, sodium oxalate, calcium phosphate, etc.); the mechanical strength of the PAS resin is deteriorated (zinc oxide, zinc carbonate, .alpha.-alumina, etc.); and although they have a good corrosion-inhibiting effect, the melt-flow characteristics and crystallization properties of the PAS resin are lowered in that the melt viscosity of the PAS resin is increased to a significant extent and/or its crystallization speed is reduced to a great extent, and hence its processability is deteriorated (the hydroxides or oxides of Group IIA metals of the periodic table, sodium citrate, metal aluminates, sodium carbonate, lithium carbonate, sodium chromate, etc.), or toxicity is high (sodium chromate and ammonium chromate). There has not been provided under the circumstances any corrosion inhibitor which can fully satisfy in practical use.